Research related to radio frequency identification (RFID) is rapidly developed in recent years. RFID composed of a tag and a reader is a non-contact, automatic identification technology. Refer to FIG. 1 showing a schematic diagram of a conventional high-frequency RFID receiving device 2 capable of receiving a signal from an RFID reader or an RFID tag via an antenna 3. The signal is transmitted to a decoder 6 after processed by an analog circuit 4 and sampled by a sampling circuit 5.
Generally speaking, the decoder 6 of the high-frequency RFID receiving device 2 applies a correlation method for decoding a header segment and a data segment of the signal. However, decoding errors frequently occur during decryption on the data segment of the signal. The reason for decoding errors is that, whether a digital logic level of a bit in the data segment is 0 or 1 is determined by the decoder 6 according to whether a correlation peak value generated by the bit is greater than a threshold. The result from the decoder 6 determining the digital logic level of the bit has an inseparable relationship with the setting of the threshold of the correlation peak value. Thus, when the threshold is set too low or too high, a decoding error occurs due to incorrect determination made by the decoder 6.
Therefore, it is one of the objectives of the invention to provide a decoding apparatus and a method to solve the problem mentioned above.